This application is a 371 of PCT/AU98/00588.
The present invention relates to a process for purifying biological molecules from food process streams and to the biological molecules prepared by the process.
The food processing industry, particularly, the dairy and the sugar refining industries, generates substantial quantities of aqueous by-product solutions and extracts (process streams), which can present a serious waste disposal problem but which also represent a rich source of nutrients such as sugars, proteins, peptides, minerals, vitamins, etc. By extracting the valuable nutrients from the aqueous process streams before disposal, the environmental impact of such wastes can be minimised.
Methods for extraction of sugars from aqueous food processing streams or extracts, based on chromatographic separation procedures, have been described for sucrose molasses, whole whey, milk, and lactose molasses etc. The methods that make use of chromatographic procedures, particularly ion exclusion chromatography, have the disadvantage of not being able to resolve clearly the peaks of ionic materials from non-ionic materials in the presence of divalent cations. The process comprises, at least in part, subjecting the process stream to an ion exclusion chromatography step using a chromatography column comprising a strong cation resin in the monovalent metal form. As the magnesium and/or calcium ions contained in the process stream exchange with the monovalent metal ions on the cation resin, the separating capability of the cation resin is progressively reduced. This necessitates periodic interruption of the purification procedure to regenerate the cation exchange resin which in turn involves consumption of regeneration reagents thus resulting in the generation of further waste material requiring disposal and the reduction in the productivity of the process.
A process developed for the processing of sugar factory molasses includes an ion exchange pre-column charged with sodium and/or potassium ions which is designed to remove calcium and/or magnesium salts from the molasses before it is subjected to further chromatographic separation to purify the desired sugar. In this process, the pre-column which after a time becomes saturated with calcium and magnesium ions, thus losing its effectiveness, is xe2x80x9crechargedxe2x80x9d or regenerated with monovalent metal ions by recycling through the pre-columns the monovalent ion fraction obtained from the chromatography column.
However, the purification procedures which may be applicable to a particular process stream may not be easily adapted for use with process streams which have origins in a different industry. Thus, a method developed for purification of sugars from, for example, sugar factory molasses cannot be applied to purification of sugars from, for example, dairy process streams because of the differences in the nature and content of other organic and inorganic molecules present in the process streams. For example, it has been found that the monovalent ion fraction obtained from chromatographic separation of process streams with a high content of phosphate, which when this fraction is used to regenerate the pre-column, interacts with calcium in the pre-column and precipitates, thus blocking the column and reducing its efficiency.
There is, therefore, a need for a chromatographic process for isolation of valuable nutrients and minerals which is applicable to food processing streams generally, and which does not have the above mentioned disadvantages.
Thus, it is the object of the present invention to overcome or at least ameliorate some of the disadvantages of the prior art discussed above, or to provide a useful alternative.
According to a first aspect there is provided a separation process including the steps of:
a) contacting an aqueous solution including a nutrient and divalent ions with an ion exchange resin including monovalent ions, until the concentration of divalent ions in said aqueous solution has been depleted in comparison to the initial concentration of divalent ions in said aqueous solution and collecting the eluate;
b) subjecting the eluate from step (a) to a process capable of separating monovalent ions to obtain a permeate fraction including monovalent ions and a retentate fraction including said nutrient;
c) separating the retentate fraction from step (b) into fractions, wherein at least one of said fractions includes the major portion of said nutrient,
d) regenerating the ion-exchange resin in step (a) by contacting the ion-exchange resin with a solution including the permeate fraction from step (b) until a major portion of divalent ions in the ion exchange resin have been replaced by monovalent ions.
The divalent ions may be primarily calcium and/or magnesium, and the monovalent ions may be primarily sodium and/or potassium.
For preference, the process for separating monovalent ions is a membrane process and more preferably it is nanofiltration. However other processes which would be equally effective would be clear to a skilled addressee from the teaching herein.
It will be understood that more than one fraction in step (c) of the process could contain nutrients of interest which may be isolated and purified by the process. Also, one of the fractions in step (c) is preferably ionic and may contain ionic nutrients such as minerals whereas the other is preferably non-ionic and may contain non-ionic nutrients such as sugars.
It will be understood that in other embodiments of the invention nanofiltration of the aqueous solution may be conducted before step (a) and the nanofiltration permeate may be used subsequently to regenerate the ion-exchange resin used in step (a).
Preferably the separation step (c) is performed on an ion exclusion resin.
Optionally a number of additional separation and purification steps may be used in the process, as outlined for example in FIGS. 1 to 4.
According to a second aspect there is provided a nutrient prepared by the process according to the first aspect.
The nutrients which may be extracted by the process to a very high level of purity are carbohydrates (including sugars), vitamins, peptides, proteins, minerals and the like.
Preferred feed streams which can be used in the process of the present invention are dairy process streams containing lactose and minerals such as sweet cheese whey permeate, acid whey permeate, milk permeate, and mother liquor from lactose crystallisation process.
Other feed streams containing sugar and minerals which can also be used are raw beet and cane juice extracts, beet and cane molasses, hydrolysed starch and the like. Also, miscellaneous extracts of plants including fruit and vegetable juices, extracts of animal products or extracts of microbial origin including fermentation products may be used with the process of the present invention.
Minor variations and adaptations of the process which may be required for purification of a desired nutrient from different food processing streams would be clear to a skilled addressee from the teaching provided in the present specification.
Unless the context requires otherwise, throughout the specification, and the claims which follow, the words xe2x80x9ccomprisexe2x80x9d, and the like, are to be construed in an inclusive sense, that is as xe2x80x9cincluding, but not limited toxe2x80x9d.